(1) Field of the Invention
The present invention relates to high velocity underwater projectiles and more specifically to an underwater projectile configuration that includes a cylindrical telescoping cavitator piston design capable of changing the shape of the projectile nose where such change to the projectile nose tip geometry results in a controllable supercavitation produced vaporous cavity that reduces projectile drag resistance while maximizing projectile range and where the projectile nose tip further includes a retractable piston feature. The projectile nose is designed to house a cylindrical cavitator piston that protrudes forward from the projectile at launch. Velocity induced forces on this cavitator piston cause the piston to gradually retract into the projectile nose, until a larger, secondary cavitator is exposed to the vaporous cavity.
(2) Description of the Prior Art
The U.S. Navy is developing underwater gun systems for use in anti-mine and anti-torpedo operations. A basic gun system includes underwater ballistic projectiles, an underwater gun, a ship-mounted turret, a targeting system, and a combat system. The underwater gun shoots the underwater projectiles that are specially designed for rapid neutralization of undersea targets at relatively long ranges of up to 200 meters. The undersea targets are identified and localized with specialized targeting systems, and the combat system provides the control commands to direct the ship-mounted turret to point the gun towards the target.
Referring now to FIG. 1, there is shown a typical prior art tapered supercavitating projectile generally identified as 10. Projectile 10, once fired from an underwater gun, can accurately travel relatively large distances by making use of the phenomenon known as the supercavitation effect. Supercavitation occurs when projectile body 12 travels through water 14 at very high speeds and a vaporous cavity 16 forms at its forward tip 18. With proper projectile design, the vaporous cavity can extend back beyond the projectile back end 20 so as to envelop the entire projectile. Because the enveloped projectile is not in direct contact with the water, excluding the small cavitator tip and an occasional collision with the cavity wall, known as “tail slap”, the viscous drag on projectile body 12 is significantly reduced over the drag that would be experienced by a fully wetted projectile body.
FIG. 2a shows an alternate tapered supercavitating projectile shape generally referred to as 40. At launch, a vaporous cavity 16 is formed, the size of which is a function of the projectile speed and the projectile size and shape. As a typical supercavitating projectile 40 begins to travel down-range, it starts to slow down due to the drag generated at its tip and the corresponding cavity shrinkage that the drag generates. Cavity 16 continues to shrink as projectile 40 decelerates until the cavity can no longer envelop the entire projectile at which point drag greatly increases and the projectile slows dramatically. The prior art has also postulated that a secondary cavitator 42, aft of primary cavitator 44, and representing a step in the projectile 46 body profile, can be used to continue to produce a cavity 16 after the cavity from primary cavitator 44 shrinks below a certain point. This effect is shown in FIG. 2b where a shrinking forward cavity segment 16a continues to collapse while cavity 16 transitions to secondary cavitator 42 and extends aft to continue to envelope the bulk of projectile 46.
The difficulty with this fixed geometry approach is that very tight tolerances must be maintained in the location and size of the secondary cavitator 42 for it to be effective. If cavitator 42 is too large or placed too far forward it will interfere with cavity generation by the primary cavitatator 44. If it is too far aft or too small, it will never engage the cavity boundary and the cavity will close on the afterbody 46 of projectile 40 rather than on secondary cavitator 42.
What is needed is to improve the stepped cavitator concept in such a way as to improve its effectiveness throughout the supercavitating projectile's flight.